In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, it is considered to introduce communication between devices (Device to Device: D2D) as a new function to be specified in Release 12 or subsequent versions (see Non Patent Literature 1).
In the D2D communication, a plurality of neighboring user terminals perform direct communication without passing through a network. That is, a data path of the D2D communication does not pass through the network. On the other hand, a data path of normal communication (cellular communication) of a mobile communication system passes through the network.